A strand-elongation initiated DNAzyme walker for terminal deoxynucleotidyl transferase activity detection

Abstract

Terminal deoxynucleotidyl transferase (TdT) is a DNA polymerase found to be overactive in most leukemia cells and is recognized as a biomarker of leukemia. Here, we develop a strand-elongation initiated DNAzyme walker to detect TdT activity. The walker is constructed by modifying specially designed track strand (TS) and incomplete walking strand (WS) onto the surface of a mesoporous silica nanoparticle (MSN) loaded with large amounts of rhodamine 6 G (Rh6 G) in its pores. The TS is a hairpin DNA with an RNA cleavage site, serving as substrate for DNAzyme and encapsulating the Rh6 G. The incomplete WS contains one side of binding arm and partial catalytic core of DNAzyme. Under the action of TdT, the incomplete WS is elongated with polyA, completing the lacking part of catalytic core and the other side of binding arm of DNAzyme. Then the completed DNAzyme cleave the TSs, unblocking and releasing the Rh6 G to indicate the TdT activity. This walker is completed and initiated only after the action of TdT, ensuring its strict specificity for TdT activity. Besides, each WS cleave multiple TSs, and each cleavage leads massive Rh6 G to be released. Such double-amplified signal accumulation endows the walker with good sensitivity. This walker specifically detected TdT activity down to 0.093 U mL−1, and successfully detected TdT activity in human serum. The proposed walker demonstrates a novel method for specific and sensitive detection of TdT activity, providing an effective tool for TdT-related biological research and leukemia theranostics.